But isnt it still possible that a celestial body made out of quarks or maybe something even denser becomes heavy enough to swallow sun-light as well as all the other things?
Yes, and if that happens, then by definition it becomes a black hole. The reason they're called black holes is because their gravity is so intense that not even light can escape them. That's the whole point of the name. Anything that has an escape velocity greater than the speed of light IS a black hole by definition, regardless of how it forms.
It`s also possible that there is a limit to mass-density that is not indefinite or involves singularity.
As I said, the only possible limit is quantum uncertainty. Since there's a Planck-scale indeterminacy in the position or momentum of any particle, that would mean that you could never really say that every particle in the black hole occupied the exact same point. So that would result in enough of a "blur" to prevent the formation of an actual singularity. However, since we as yet have no reliable theory that unifies general relativity (which describes gravitation and is the basis of black hole physics) with quantum mechanics, we can't say for sure that this is the case. It's been an open question in black-hole physics for decades.
Such a scenario would make it theoretically possible to carve out a peace of a black hole (Or maybe blow it up so that its separated into smaller junks of mass who have little or no gravity on their own) and put a peace of it on display back home. "Absolute mass! Very dense! Come look at it!"
Uhh, no. Remember, the reason light can't escape from it is because its gravity is so intense that its escape velocity is greater than the speed of light. And since nothing can travel faster than light relative to the space it occupies, it is impossible for any "pieces" to be removed. The only way a black hole can lose mass is through Hawking radiation, a process that happens right at the event horizon and causes the BH to lose mass through quantum processes. And as
Great Mambo Chicken says, that only happens with the small ones.
If all black holes are singular in their tiny-ness, wouldnt that make all of them completely equal? I read somewhere that there probably is a "super-heavy" black hole in the midle of our galaxy that we revolve around, but if all black holes are equal, than one of them cant be any more "superheavy" than the others.
No, that's completely incorrect. You've got to stop using the word "heavy," because it's the wrong word here and it's leading you to confuse two separate concepts, mass and density. Mass is how much matter a thing contains; density is how tightly packed it is. A 1-pound bag of, say, popcorn is a lot bigger than a 1-pound lead weight, because it's much lower in density -- that 1 pound worth of material is a lot less tightly packed. Same mass, different densities. By the same token, two things can have the same density but a different mass -- like a 1-pound lead weight versus a 50-pound lead weight.
So yeah, black holes all have infinite density or as close to it as quantum mechanics allows, but they can have any mass, from subatomic to near-galactic.
If we have a black hole, and then some pretty advanced civilisation wants ro remove it, or turn it into something visible. (maybe they just really hate black holes) Could they use anti-matter to do so?
The ball of anti-matter removes the same amount of mass as itself contains upon impact, thereby reducing the black hole in size.
I think you're suggesting that the antimatter would annihilate with an equivalent amount of matter. But that wouldn't work. Matter-antimatter annihilation doesn't just produce nothingness. It converts the mass to energy, and that energy radiates out in the form of particles -- gamma-ray photons for electron-positron annihilation, or gamma rays, pions, and neutrinos for proton-antiproton annihilation.
But -- inside a black hole, that radiation has nowhere to go. It can't escape the event horizon, because it only travels at or below the speed of light. It just stays trapped along with everything else, and since mass and energy are equivalent, the mass of the black hole remains unchanged.
Since it also makes it loose gravitational pressure, it might start to grow, changing the properties in mass while doing so. Mass doesnt like to be squeezed together, so the densified mass might want to go back to earlier states such as quarks, neutrons, and then atoms with electrons.
Might such a event cause the life of the black hole to reverse in a way? Maybe it will end up as a big hydrogen star again?
That could happen if, say, a chunk of neutronium were blasted off of a neutron star. Without sufficient gravity to keep it compressed, it would expand back to a non-degenerate state. But not with a black hole, ever.
Nothing can escape from a black hole. Once it's inside the event horizon, it's there forever.
What if you threw anti-matter into a quark star? Could you reduce its mass so that it started to grow it into a big hydrogen-star or something similar, big and shiny? Creating fresh stars out of old and broken ones would be kind of like doing the universe a favor.
A quark star doesn't have an event horizon, so yes, it could lose material. Any normal antimatter you dumped onto it would get compressed into antineutrons or antiquarks, but the antiquarks could annihilated with the quarks in the star and produce gamma rays and the like, which could escape. But all you'd do is shrink the quark star, and maybe release dangerous chunks of strange-quark matter into the galaxy. (Strange matter's dangerous because it can turn anything it touches into more strange matter.) Unlike neutronium, which can (I think) expand back to normal matter, quark matter would keep its nuclear density even if broken into small pieces.
And you couldn't magically turn a neutron star or quark star back into a hydrogen-burning star, any more than you can turn a corpse back into a living person. Even if you miraculously had enough antimatter to disintegrate a neutron star (and how you'd be able to generate such extraordinary amounts of antimatter, let alone store it safely, is a very big question), you'd just end up with a cloud of elemental material that might eventually become a small part of a stellar nursery and contribute to the mass of new stars and planets.
You see, a neutron star or black hole doesn't contain the
entire mass of the star it formed from, just its core. The bulk of the star's atmosphere is blown away in the supernova. And that's what
does contribute to the formation of new stars and planets. Supernovae are where most of the heavy elements in the galaxy are formed, so planets and people wouldn't exist without them. Our atoms were forged in supernovae.
And what happens to the mass thrown out by such a explosion?
